** Changed in: ubuntu-power-systems
Assignee: (unassigned) => Canonical Foundations Team
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zlib: improve crc32 performance on P8
Status in The Ubuntu-power-systems project:
Status in zlib package in Ubuntu:
Calculate the checksum of data that is 16 byte aligned and a multiple
of 16 bytes.
The first step is to reduce it to 1024 bits. We do this in 8 parallel
chunks in order to mask the latency of the vpmsum instructions. If we
have more than 32 kB of data to checksum we repeat this step multiple
times, passing in the previous 1024 bits.
The next step is to reduce the 1024 bits to 64 bits. This step adds
32 bits of 0s to the end - this matches what a CRC does. We just
calculate constants that land the data in this 32 bits.
We then use fixed point Barrett reduction to compute a mod n over GF(2)
for n = CRC using POWER8 instructions. We use x = 32.
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